The lipid structure and metabolism of cultured minimal deviation hepatoma cells, hepatoma grown in host, host liver, and normal rat liver are being studied. All lipid classes are being studied. All lipid classes are being examined in whole cells, organelles, and membrane fractions. Monoenoic acids from individual neutral lipid and phospholipid classes of normal liver revealed that different lipid classes exhibited different proportions of oleic and vaccenic acids that were not changed by diet. In contrast, host grown hepatoma lipid classes all contained the same ratio of oleic to vaccenic acid. Hepatoma cells cultured on several media likewise had the same ratio of oleic to vaccenic acid. The data indicated that some lipid classes from normal hepatic tissue contained much higher levels of vaccenic acid than previously thought. The data also suggested the high level of "oleic acid", one of the most commonly reported lipid abnormalities of neoplasms, may in fact represent an increase in the level of vaccenic acid. Host grown minimal deviation hepatoma contained approximately twice the level of sphingomyelin as normal or host liver. The spingomyelin of the hepatoma contained a C-24 dienoic acid not found in the normal host liver. Examination of the sphingomyelin fatty acids from 10 other neoplasms revealed that all of the transplantable tumors contained the tetracosadienoic acid. The data suggest that a metabolic abnormality may exist in synthesis of sphingolipids of neoplasms. The studies carried out thus far have shown that the lipid metabolism in this minimal deviation hepatoma differ from that of host or normal liver. Work is continuing to explain the reason for the observed differences.